This .[.invention.]. .Iadd.application is for a reissue of U.S. Pat. No. 3,898,690 on an invention which .Iaddend.relates to rotating magnetic memories for digital data processing systems, and more particularly to apparatus for dividing (sectoring) a rotating memory into equally time spaced sectors.
In rotating magnetic memories, such as magnetic drum or disc files, it is advantageous to divide the tracks into equally time spaced sectors. Each sector may then be used to store one or more bytes, each byte consisting of a predetermined number of binary digits (bits). One approach represented by U.S. Pat. No. 3,105,228 has been to read evenly spaced pulses stored on a separate track, and to employ those pulses to synchronize a local oscillator the output of which is then used to cyclically count down from an index a predetermined number of pulses for each sector. The problem with that approach is the need to dedicate a track of the magnetic recording media and sophisticated read electronics to develop sector timing signals.
Another similar approach has been to format the sector timing information with the data information. This requires additional format decoding electronics and also uses some of the data storage space on the data tracks of the magnetic memory. That, and additional tolerances of compatibility requirements to reading recorded data on other memory devices.Iadd., .Iaddend.reduces the total data storage capacity of the magnetic memory.
Others have employed a separate disc with slots to divide the data tracks directly into sectors, one slot for each sector. This technique has the advantage of not using up part of the memory capacity, but lacks the ability or versatility of dividing one revolution of the rotating magnetic memory into any desired number of sectors. What is desired is a system that is both versatile and precise, and does not require any of the data storage space on the record media.